This invention relates to coated particles used in binding assays. It also relates to the process for making said particles and the process for using said particles.
Binding assays, including immunoassays, are commonly used medical diagnostic tools for determining the presence, and the concentration, of various analytes. Immunoassay procedures have been known for many years and include the earlier manual procedures followed by the more recent automated procedures (e.g., those run on the Bayer ACS:180(copyright) and ADVIA(copyright) Centaur(trademark) Instruments).
One of the components used in the immunoassays is a solid phase, frequently a paramagnetic particle (PMP), which is prepared by coating a magnetic particle with a material which allows further reaction of the magnetic particle with active ingredients used in the immunoassay. In the past, the magnetic particle has been frequently coated with bovine serum albumin (BSA). However, the particles coated with BSA have occasionally been found to be unstable and to yield unreliable assay results. In addition, the use of BSA alone results in high non-specific binding.
It has been found that casein and salts of casein are useful as replacements for, or in addition to, BSA as materials for coating solid phases, particularly magnetic particles, used in immunoassays and other binding assays for separation of the desired analyte. By using casein, immunoassays having improved stability and less sample discordance have been developed. Casein used at a concentration of approximately 0.05-4.0 grams per gram of paramagnetic particle (optimally approximately 0.78-1.2 grams of casein per gram of magnetic particle) has been found to confer this benefit.
In addition, a process for coating solid phases has been invented, said process comprising the mixing of casein with magnetic particles at 30-60xc2x0 C. for 5-180 hours, said process resulting in casein-coated paramagnetic particles which either (1) already have combined therewith active ingredients needed in the binding assay or (2) are capable of reacting with active ingredients needed in the binding assay.
Furthermore, a process for using the casein-coated paramagnetic particles has been developed, said particles being directly or indirectly combined with active ingredients used in the immunoassays.